In most Prestashop templates to customize the logo of the topic happens to be in JPG format so transparent become white canvases. To use images with transparency (PNG), we must perform the following steps:
Edit header.tpl template file we have activated
Find the line where the logo image: <img class=“logo” src=”{$ img_ps_dir logo.jpg} {$ img_update_time}” …
Replace logo.jpg by logo.png